Photo-induced degradation of some flavins in aqueous solution

Abstract The blue-light induced photo-degradation of FMN, FAD, riboflavin, lumiflavin, and lumichrome in aqueous solution at pH 8 is studied by measurement of absorption coefficient spectral changes due to continuous excitation at 428 nm. The quantum yields of photo-degradation determined are ϕ D (riboflavin, pH 8) ≈ 7.8 × 10 −3 , ϕ D (FMN, pH 5.6) ≈ 7.3 × 10 −3 , ϕ D (FMN, pH 8) ≈ 4.6 × 10 −3 , ϕ D (FAD, pH 8) ≈ 3.7 × 10 −4 , ϕ D (lumichrome, pH 8) ≈ 1.8 × 10 −4 , and ϕ D (lumiflavin, pH 8) ⩽ 1.1 × 10 −5 . In a mass-spectroscopic analysis, the photo-products of FMN dissolved in water (solution pH is 5.6) were identified to be lumichrome and the lumiflavin derivatives dihydroxymethyllumiflavin, formyllumiflavin, and lumiflavin-hydroxy-acetaldehyde. An absorption and emission spectroscopic characterisation of the primary photoproducts of FMN at pH 8 is carried out.

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